Cam drives for fuel injection pumps or the like and method of making waved cam wheels for such drives



Oct. 16, 1962 w. VOGEL 3,058,369

CAM DRIVES FOR FUEL INJECTION PUMPS OR THE LIKE AND METHOD OF MAKING WAVED CAM WHEELS FOR SUCH DRIVES Filed Nov. 17, 1959 FIG. I

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INVENTOE' 2 W/LHELM VOGEL United States Patent 3,058,369 CAM DRIVES FOR FUEL INJECTION PUMPS OR THE LHQE AND METHOD OF MAKING WAVE!) CAM ELS FOR SUCH DRIVES Wilhelm Vogel, Stuttgart-Bad Cannstatt, Germany, assignor to Robert Bosch G.m.b.I-l., Stuttgart, Germany Filed Nov. 17, 1959, Ser. No. 853,518 Claims priority, application Germany Nov. 24, 1958 7 Claims. (Cl. 74-667) The present invention relates to cams in general, and more particularly to a cam drive which may be utilized in fuel injection pumps of internal combustion engines or the like.

In the manufacture of fuel injection pumps for multicylinder internal combustion engines, it is customary to employ a discoid cam, also known as waved or crown cam wheel, which is rotated by the drive shaft of the fuel injection pump and transmits rotary motion to the injection piston. The undulate cam surface or end face of the discoid member is permanently biased 'mto engagement with one or more radially arranged rollers or reaction members which impart to the cam an oscillatory movement to axially shift the injection piston in a predetermined rhythm at which the piston delivers fuel into the engine cylinders. The cam surface of the discoid member is formed with a series of projections which, when engaging with the roller or rollers, cause axial movement of the discoid cam and of the injection piston. A gradual axial movement may be brought about by suitable shaping of the cam surface, namely, by forming the cam surface with a series of concave or convex zones or segments whose adjacent edges meet in rather sharp ridges, particularly at points closer to the axis of the discoid cam wheel, over which ridges the roller or rollers must pass when the cam wheel rotates. The curvature of the concave or convex zones or segments on the cam surface at points adjacent to their meeting edges is considerable, i.e. the radii of curvature are small, which also contributes to the formation of rather sharp ridges between the individual concave or convex zones of the composite cam surface. Whenever a roller travels over one of such sharp ridges, and also while the roller passes over the more curved zones of the cam surface which are closely adjacent to the ridges, the material of the cam wheel is subjected to very large specific compression loads or stresses (known as Hertzian pressure), which lead to rapid destruction of the cam wheel.

An important object of the present invention is to provide an improved cam drive consisting of a waved cam wheel and a follower assembly therefor which is constructed in such a way that the cam wheel is subjected to lesser stresses and can stand much longer wear and tear in actual use.

Another object of the invention is to provide a cam drive of the above outlined characteristics in which the so-called Hertzian pressure upon the cam surface segments of increased curvature is reduced to a permissible level.

A further object of the invention is to provide an improved waved cam wheel which is particularly suitable for driving the pistons of injection pumps in multicylinder internal combustion engines.

An additional object of the invention is to provide a method of extending the useful life of waved cam wheels for use in cam drives of the above outlined character.

With the above objects in view, the invention resides in the provision of a cam drive which comprises a socalled waved cam wheel member and a follower member therefor, at least one of said members being rotated and both members being constantly biased into engagement with each other so that the roller or rollers of the follower member constantly contact an undulate cam surface of the cam wheel member. In accordance with my invention, the cam surface consists of several concave or convex zones or segments whose meeting edges are partially removed, such as by grinding or in any other suitable way, whereby to eliminate such portions of the cam wheel where the Hertzian pressure would normally exceed the permissible magnitude.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of a specific embodiment when read in connection with the accompanying drawing, in which:

FIG. 1 is side elevational view of the improved cam drive; and

FIG. 2 is front elevational view of the cam drive as seen in the direction of arrow II in FIG. 1.

Referring now in greater detail to the drawing, and first to FIG. 1, there is shown a cam drive CD which is mounted in a schematically represented frame 1. The latter may constitute the housing of a fuel injection pump for multicylinder internal combustion engines whose nonrepresented fuel distributing and injecting piston is connected to the driven shaft 3 of a waved cam wheel 4. The shaft is free to rotate and to perform axial movements in a schematically indicated bearing element 112. A resilient member shown here as a helical spring 5 constantly biases the wavy or undulate composite cam surface or end face 6 of the wheel 4 into engagement with a follower consisting of four cylindrical rollers or reaction members 2 which are rotatably mounted in suitable bearings in of the frame member 1. The axes of rollers 2 extend radially with respect to the axis of the cam wheel 4, and the rollers are shown as equidistant from each other.

The annular cam surface or end face 6 comprises four concave, arcuate zones or segments 6a which, for reasons apparent later, may also be referred to as arcuate, third face portions. These surface segments or arcuate third face portions 6a cause the cam wheel 4 to perform axially reciprocating movements during each of its revolutions as the rollers 2 slide along the surface segments 6a. Each pair of adjacent segments or third face portions 6a meets in a radial ridge or projection 7 whose inner portion 7a, i.e. that portion of each projection which is closer to the axis of the cam wheel 4, is normally rather sharp, and the curvature of surface segments 6a increases at points adjacent to each of the projections 7. In other words, the radii of curvature of the segments or third face portions 6a adjacent to the ridges or projections 7 are smaller than at the points more distant from said projections. This gives rise to considerable pressure upon the cam wheel 4- whenever a roller 2 travels over the surface portions of greater curvature and over the sharp portions 7a of the projections 7 therebetween. Such pressures, called Hertzian pressures, cause rapid destruction of the cam wheel 4 and necessitate frequent dismantling of the apparatus in which the cam drive is installed. In the illustrated embodiment, the wheel 4 performs four axially reciprocating movements during each full revoluton, and causes similar movements of the shaft 3 to which the piston of a fuel injection pump may be connected.

The sharp portions 7a of projections 7 are indicated in FIGS. 1 and 2 in phantom lines because they are actually removed before the cam wheel is put to use. Thus, in accordance with the method of my invention, the useful 'ice life of the cam wheel 4 may be extended by removing the sharp portion 7a on each projection 7, i.e. by forming the latter with a substantially flat inner, first face portion 7b.

In other words, my novel method contemplates the removal of such part of each projection 7 which causes generation of excessive Hertzian pressures upon contact with the rollers 2 of the follower member. Instead of having a sharp ridge 7a, each projection 7 is thus formed with a substantially fiat, first face portion 7b at a point closer to the axis of the wheel 4. The first face portions 7b are not in the path of rollers 2', i.e. the sharp edge portions 7a are removed to such an extent that the rollers 2 contact only arcuate outermost or second face portions 70 of the projections 7. Smooth transitions are provided between the arcuate second face portions 70 and the arcuate third face portions 6a. The removal of portions 7a may be brought about by grinding or in any other suit able Way.

It will be seen that the present invention considers removal of such parts on each projection of a waved cam wheel which would cause excessive Hertzian pressures and would bring about rapid wear and tear of the assembly. Despite such removal of the sharp inner portion 7a on each projection 7, the entire width of the cam surface 6 remains intact at such points which are in contact with the rollers 2 when the piston of a fuel injection pump connected with the shaft 3- -exerts a maximum operating pressure, i.e. the removal of the parts 7a in no way weakens the cam wheel 4. This is due to the fact that maximum operating pressures in a fuel injection pump do not arise at a time when the injection piston reaches that end of its stroke which coincides in time with the contact of a roller 2 with a selected projection 7.

Of course, in another type of cam drive, the wheel 4 may remain stationary and may impart reciprocating movements to a rotary follower assembly whose roller or rollers engage with its earn surface.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this inventon and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A cam drive, particularly for injection pluugers of fuel injection pumps in internal combustion engines, comprising a wheel-shaped cam member having an end face and comprising a plurality of spaced radially extending projections at said end face, each of said projections having an inner portion and a ridge-like outer portion extending radially outwardly from the respective inner portion, said end face having a plurality of substantially flat first face portions extending along the inner portions of said projections, a plurality of arcuate second face portions extending along the outer portions of said projections, and a plurality of arcuate third face portions extending between and having smooth transitions into said second face portions; at least one rotary reaction member having a peripheral surface portion and rotatable about an axis extending radially with respect to the axis of said cam member; means for permanently biasing one of said members against the other member so that the peripheral surface portion of said reaction member abuts against the end face of said cam member; means connected to one of said members for rotating said one member about the axis of said cam member so that the peripheral surface portion of said reaction member rolls along and is in linear contact with the second and third portions but remains out of contact with the first portions of said end face, whereby Wear caused by Hertzian pressure is reduced; and means for supporting said members so that one thereof is reciprocable with respect to the other member in the axial direction of said cam member when said peripheral surface portion rolls along the second and third portions of said end face.

2.. A cam drive as set forth in claim 1, wherein the sharpness of said ridge-like outer portions diminishes in a direction radially outwardly from the respective inner portions.

3. A cam drive as set forth in claim 1, wherein said rotating means comprises a driven shaft coaxially connected with said cam member.

4. A cam drive as set forth in claim 3, wherein said supporting means comprises fixed bearing means for said reaction member and bearing sleeve means for said shaft, said resilient means constructed and arranged to bias said cam member against said reaction member.

5. A cam drive as set forth in claim 4, comprising a plurality of equally spaced reaction members.

6. A cam drive as set forth in claim 1, wherein the peripheral surface portion of said reaction member is cylindrical.

7. A cam drive as set forth in claim 6, wherein said third end face portions are of concave shape and wherein said second end face portions are of convex shape.

References Cited in the file of this patent UNITED STATES PATENTS Sons (1956); section 10.3 relied upon. 

